1. Field of the Invention
This invention relates to a sweeping machine with variable wheel tracking.
Small compact sweeping machines are well known in the marketplace and comprise a four-wheeled vehicle with a cab at its front end behind which is a rubbish hopper capable of taking up to about a ton of rubbish or other material, the machines having steerable front wheels controllable from the cab and a pair of contra-rotating brushes extending forwardly in front of the cab and easily visible to the operator within the cab. The brushes are able to sweep a width varying from about 1 meter to 2 meters, the width of which is again controllable from within the cab. The machines are normally provided with a suction arrangement to pick up rubbish swept to a central location between the contra-rotating brushes and with some form of dust separation equipment to separate out dust from the exhaust air stream from the suction arrangement. The machines may be provided with other operator comforts such as full suspension, electronic control systems for reduced operator workload, heated windscreen, adjustable steering wheel, adjustable driver's seat, a forward tilting cab and air conditioning. It is also important that the machine has excellent operator visibility. In order to improve rear vision, a reversing camera may also be provided. It is also preferable to provide the machines with four-wheel drive to improve stability in wet conditions and for good kerb climbing.
2. Description of Related Art
The machine of the present invention is of the compact type and accordingly it needs to have a narrow wheel track to allow it to fit between bollards in shopping precincts, to allow it to sweep on foot paths and generally to minimise the disruption of pedestrians. However, because of the requirement for the narrow wheel track, and because of the weight of the rubbish which can be carried in the rubbish hopper behind the operator which hopper necessarily needs to sit in a upper area of the machine, the machine tends to be unstable and prone to tipping over. To prevent this tendency, manufacturers have in the past tried to lower the centre of gravity, but in a small compact machine this is not particularly easy, especially if the machine is to carry up to a ton of rubbish. Accordingly, in order to prevent tipping over of a full machine, it has been necessary in the past for manufacturers to have to limit the speed of the machine to approximately 10 miles per hour. However, when the speed of the machine is limited, this means that it takes some considerable time for the machine to travel to and from the job, i.e. from the depot of the local council to a city centre. Furthermore, of course, it also takes the machine some considerable time to return to the depot to tip the contents of the hopper once it is full. Accordingly, small or compact slow sweeping machines are not attractive and there is a requirement for a small fast sweeper, but it has to be safe and stable when it is travelling fast.